1. Field of the Invention
The present invention relates to a sol-gel liquid used when forming an electromechanical conversion element, an electromechanical conversion element formed with the sol-gel liquid, a liquid discharge head using the electromechanical conversion element, and an inkjet recorder having the liquid discharge head.
2. Description of the Background Art
Forming a thin film of a metal complex oxide by sol-gel methods is known, as disclosed in K. D. Budd, S. K. Dey, D. A. Payne, Proc. Brit. Ceram. Soc. 36, 107 (1985). Forming a self-assembled Mon-layer (SAM) on an Au film with alkanethiol is also known, as disclosed in A. Kumar and G. M. Whitesides, Appl. Phys. Lett., 63, 2002 (1993).
Japanese published examined application No. 4-168277 (JP-H04-168277-A) discloses forming a thick film of a complex oxide on a substrate by sol-gel methods, which is used for a space light modulation element, an actuator of an inkjet printer head, and a sensor. Japanese published unexamined application No. 2003-297825 (JP-2003-297825-A) discloses discharging different sol-gel liquids from two or more inkjet heads to form a ferroelectric thin film in a plane, in which the liquids are uniformly mixed.
International publication No. 2003/098714 discloses a typical configuration of liquid spray head using a piezoelectric thin film.
Japanese published unexamined application No. 2006-176385 (JP-2006-176385-A) discloses a precursor composition for forming a ferroelectric film, a method of preparing the precursor composition, and a precursor composition ink for inkjet application.
Having many advantages, such as scarcely making noise, being capable of printing at high speed, and even being capable of using many kinds of inks printable on inexpensive plain paper, inkjet recorders having an inkjet head are widely used in image forming apparatuses (image recorders) such as printers, facsimiles, and copiers.
The liquid discharge head of the inkjet recorder has a nozzle discharging an ink drop, a pressure chamber (also referred to as a pressurization chamber, a pressurization liquid chamber, a liquid chamber, a discharge chamber, or an ink flow path) connected with the nozzle and a pressure generator pressurizing ink in the pressure chamber to be discharged from the nozzle.
The pressure generator includes both a piezo type, deforming and displacing an oscillation board forming one wall of the pressure chamber to discharge ink drops, using an electromechanical conversion element such as a piezoelectric element; and a bubble (thermal) type generating bubbles with a film by boiling an ink to discharge ink drops, using an electrothermal conversion element such as a heating resistor in the pressure chamber. Further, the piezo type includes a longitudinal oscillation type using deformation in d33 direction, a lateral oscillation (bend mode) type using deformation in d31 direction and a shear mode type using shear deformation. Lately, progress in semiconductor processing and MEMS development has progressed to the point where a thin film actuator in which a pressure chamber and a piezo element are directly formed on a Si substrate are being planned.
FIG. 1 is an embodiment of the liquid discharge head using the electromechanical conversion element. The electromechanical conversion element has a layered structure including a lower electrode, an upper electrode, and an electromechanical conversion film therebetween. (For ease of illustration, a liquid feeder, flow paths, etc. are omitted.)
FIG. 2 is an embodiment including plural liquid discharge heads shown in FIG. 1. Each pressure chamber includes an individual electromechanical conversion element for generating pressure to discharge ink.
The electromechanical conversion film is formed of lead zirconate titanate (PZT), barium titanate, etc. These include plural metal oxides as a main component and are typically referred to as metal complex oxides.
Conventionally, an electromechanical conversion film material is deposited on a lower electrode by known film forming technologies such as vacuum film forming. Patterning of the upper electrode is made by photolithographic etching after forming the upper electrode. Patterning of the electromechanical conversion film and the lower electrode are similarly made to form an electromechanical conversion element.
However, dry etching of the metal complex oxides, particularly PZT, is not easy, and a specific type of reactive ion etching (RIE) combining ICP plasma, ECR plasma and helicon plasma is needed, resulting in a cost increase for the production apparatuses.
Individualized PZT film forming methods include a hydrothermal synthesis method selectively growing PZT on a Ti metal. The resultant PZT film needs a thickness not less than 5 μm to have sufficient pressure resistance (an electric field applied to the PZT film easily breaks down a film having a thickness less than 5 μm), and thus cannot have a desired thinness. When the element is formed on a Si substrate, the Si substrate needs protection because the hydrothermal synthesis is performed under a strongly-alkaline aqueous solution. Other methods include vacuum deposition methods and AD methods, but as a practical matter both of them have too many problems to use.
For these reasons, a need exists for a sol-gel liquid stably and continuously dischargeable under simple discharge conditions, when an individualized electromechanical conversion film is formed by partially modifying the surface of a lower electrode and coating the modified part with a sol-gel liquid by inkjet methods.